An epidemiologically successful Escherichia coli sequence type modulates Plasmodium falciparum infection in the mosquito midgut.

Malaria transmission relies on the successful development of Plasmodium parasites in the Anopheles mosquito vector. Within the mosquito midgut, malaria parasites encounter a resident bacterial flora and parasite-bacteria interactions modulate Plasmodium development. The mechanisms by which the bacteria interact with malaria parasites are still unknown. The intestinal microbiota could regulate immune signaling pathways or produce bacterial compounds that block Plasmodium development. In this study, we characterized Escherichia coli strains previously isolated from the Anopheles mosquito midgut and investigated the putative role of two E. coli clones, 444ST95 and 351ST73, on parasite development. Sporogonic development was significantly impacted by exposure to clone 444ST95 whereas prevalence and intensity of infection were not different in mosquitoes challenged with 351ST73 as compared to control mosquitoes. This result indicates midgut bacteria exhibit intra-specific variation in their ability to inhibit Plasmodium development. Expression patterns of immune genes differed between mosquitoes challenged with 444ST95 and 351ST73 and examination of the luminal midgut surface by transmission electron microscopy revealed distinct effects of bacterial exposure on midgut epithelial cells. The 444ST95 clone strongly affected mosquito survival and parasite development and this could be associated to the Hemolysin F or other toxins released by the bacteria. Further studies will be needed to decipher the virulence factors and to determine their contribution to the observed phenotype of the 444ST95E. coli strain that belongs to the epidemiological ST95 clonal group responsible for extra intestinal infections in human and other animals.